Structural studies will be undertaken on three different protein systems in order to better understand the molecular basis for their biological function. The first study focusses on the enzyme, mitochondrial malate dehydrogenase for which suitable crystals are already available. X-ray diffraction analysis using the method of heavy atom isomorphous replacement will be carried out at high resolution. Newly devised molecular graphics methods will be used to analyze the electron density maps and the molecular model will be compared with that of cytoplasmic malate dehydrogenase and other dehydrogenases. Such comparisons will offer some clues as to the factors important in organelle assembly. In addition studies aimed at locating the NAD ion and malate binding sites in mitochondrial malate dehydrogenase will also be carried out. In order to find the underlying basis of integral membrane protein incorporation into lamellar lipid phases, structural studies on the membrane enzyme, D-hydroxybutyrate dehydrogenase will also be undertaken. This project has two directions, one of which is to incorporate the enzyme into single-walled liposomes and observe the changes in the small angle x-ray scattering curves. This will be done with an eye toward determining the degree of insertion of the protein into the lipid bilayer. The second part focusses on the preparation of large single crystals of the enzyme with the long-range goal of observing the primary lipid binding sites on the enzyme. In order to understand lipid:protein interactions in soluble lipoprotein systems. Structural studies on the yolk lipoprotein complex will be continued. This work employs X-ray powder diffraction and modification of microcrystals to locate the lipid binding domains in the overall structure. In order to increase the chances of preparing large single crystals, the project includes an investigation of the insect and pupal lipoprotein complexes.